1. Field of the Invention
The present invention relates to temperature monitoring techniques used in electrical and/or information processing systems such as computer systems and microprocessors.
2. Description of the Related Art
High temperatures may subject electrical and/or information processing systems to a thermal runaway condition resulting in failure of one or more electronic components of such systems. For example, information processing systems often include one or more microprocessors which can be damaged by high temperatures. Such component failure often results in expensive repair or replacement of the components or of the entire system. Proper temperature monitoring is therefore critical to the continued operation of such systems, and great importance is placed on early detection of potentially damaging heat buildup.
Modern information processing systems such as computer systems and/or microprocessors often include temperature monitoring devices. For example, personal computer systems including the Pentium.TM. microprocessor or Pentium II.TM. microprocessor available from Intel Corporation of Santa Clara, Calif. often include temperature monitoring devices because the Pentium.TM. microprocessor or Pentium II.TM. microprocessor generates enough heat that thermal monitoring is required to prevent expensive failures. Real-time monitoring is especially important because of the possibility that changing ambient conditions such as in portable computer systems may increase the likelihood of thermal overload. Subsequent higher performance generations of microprocessors have dramatically exacerbated the problem of possible thermal overload.
A personal computer industry standard specification known as the Advanced Configuration and Power Management Initiative (ACPI) has been developed to outline requirements for thermal management. ACPI version 1.0 dictates that there be four thermal states: "none," "passive," "active," and "critical." In a personal computer system a "none" thermal state indicates that the thermal situation requires no special action. A "passive" thermal state typically indicates, for example, that the microprocessor(s) should be slowed down to reduce the thermal load. An "active" thermal state indicates that a fan or some other active cooling device be started. A "critical" thermal state indicates that the system is in thermal runaway and must be shut down immediately to prevent damage. ACPI also allows a software operating system to control the setting of temperature thresholds to determine the limits of the four prescribed thermal zones or levels. However, if the operating system crashes or malfunctions, the temperature of the hardware system could become unmonitored, and the computer system could become vulnerable to thermal damage.
In one temperature monitoring technique, an information processing system includes a hardware programmable thermal management integrated circuit (IC) having an on-chip, solid state temperature sensor embedded in its silicon die. The sensor senses the temperature of its own die and outputs a signal based on the sensed temperature value. Typically the thermal management IC will have one or more hardware programmable (e.g., external resistor programmed) temperature thresholds to implement the above discussed thermal zones. Using such a thermal management IC provides the advantage of an inherent reliability in that erroneous software operation does not jeopardize the thermal protection. One disadvantage to using such an IC is that the thermal management IC must be placed physically close to key integrated circuits such as a CPU for thermal coupling because the temperature sensing element is on the thermal management IC. This can be inconvenient and sometimes impossible. Another disadvantage is that this type of device is not software programmable and is therefore not in compliance with the ACPI specification.
In another temperature monitoring technique, an information processing system includes a software programmable thermal management IC having an on-chip solid state temperature sensor. Such an implementation typically includes a serial port whereby the system software can access temperature data and manipulate temperature thresholds on the fly. Such an implementation advantageously allows the system to intelligently respond to changing conditions. Also, the system may be in compliance with the ACPI specification if there are enough thresholds available to define all of the prescribed thermal levels. However, the thermal management IC also must be located so that there is a good thermal coupling to the CPU because the temperature sensing element is on the thermal management IC.
In another temperature monitoring technique, an information processing system includes a software programmable thermal management IC with off-chip sensor input and multiple thresholds. This is a desirable option because it provides increased flexibility and performance. Performance is enhanced because the sensing element (e.g., a junction diode) is located separate from the thermal management IC and is typically located on the CPU die. The thermal management IC typically connects to two pins on the CPU to access the sensing element. This allows the temperature measurement to be much more accurate because of a better thermal coupling between the CPU and the sensing element while allowing the system designer more flexibility in where the thermal management IC is located within the information processing system.